Abstract. Alloy718 has been used for many years in the aerospace industry due to its unique mechanical properties and good processing characteristics, especially its workability. However, the temperature limit of Alloy718 is about 650• C because of the thermal instability of the main strengthening phase γ -Ni 3 (Nb,Ti,Al). Numerous attempts have been made to develop a new wrought 718-type alloy for high temperature applications. The approach was to increase the stability, i.e. the solvus temperature of the γ -phase (T γ ,s ). However, this affected workability as the solvus temperature of the δ-phase (T δ,s ) did not increase accordingly so that the window for fine grain forging T δ,s -T γ ,s became smaller. In this paper the development of a new γ /γ -alloy on the basis of Alloy718 is presented, where the microstructure is stable at 800• C, mechanical properties are similar to Alloy718, yet do not deteriorate beyond 650• C, and the forging window is wider than the one of Alloy718, allowing for good workability. This was essentially achieved by the addition of about 17%-30% Co in combination with an Al/Ti-ratio of more than 5.0 and an Al-content of about 1.6%-2.2%. The key role of cobalt is to stabilize the δ-phase, allowing for solvus temperatures in excess of 1100• C. Consequently, the stability of the γ -phase can be increased by further addition of aluminium. At the same time the Ti-content is reduced to prevent formation of the η-(Ni,Co) 3 (Ti,Al,Nb) phase. Besides discussion of the alloy development concept, information on microstructure evolution and mechanical properties will be given.

Alloy718 has been used for many years in the aerospace industry due to its unique mechanical properties and good processing characteristics, especially its workability. However, the temperature limit of Alloy718 is about 650 • C because of the thermal instability of the main strengthening phase γ -Ni 3 (Nb,Ti,Al). Numerous attempts have been made to develop a new wrought 718-type alloy for high temperature applications. The approach was to increase the stability, i.e. the solvus temperature of the γ -phase (T γ ,s ). However, this affected workability as the solvus temperature of the δ-phase (T δ,s ) did not increase accordingly so that the window for fine grain forging T δ,s -T γ ,s became smaller. In this paper the development of a new γ /γ -alloy on the basis of Alloy718 is presented, where the microstructure is stable at 800 • C, mechanical properties are similar to Alloy718, yet do not deteriorate beyond 650 • C, and the forging window is wider than the one of Alloy718, allowing for good workability. This was essentially achieved by the addition of about 17%-30% Co in combination with an Al/Ti-ratio of more than 5.0 and an Al-content of about 1.6%-2.2%. The key role of cobalt is to stabilize the δ-phase, allowing for solvus temperatures in excess of 1100 • C. Consequently, the stability of the γ -phase can be increased by further addition of aluminium. At the same time the Ti-content is reduced to prevent formation of the η-(Ni,Co) 3 (Ti,Al,Nb) phase. Besides discussion of the alloy development concept, information on microstructure evolution and mechanical properties will be given.

To increase the lifetime of rocket combustion chambers, thermal barrier coatings (TBC) may be applied on the copper chamber wall. Since standard TBC systems used in gas turbines are not suitable for rocket-engine application and fail at the interface between the substrate and bond coat, a new bond-coat material has to be designed. This bond-coat material has to be chemically compatible to the copper substrate to improve the adhesion and needs a coefficient of thermal expansion close to that of copper to reduce thermal stresses. One approach to achieve this is to modify the standard NiCrAlY alloy used in gas turbines by adding copper. In this work, the influence of copper on the microstructure of NiCrAlY-alloys is investigated with thermodynamical calculations, optical microscopy, SEM, EDX and calorimetry. Adding copper leads to the formation of a significant amount of β-NiAl and α-Cr. Reducing the aluminum and chromium content leads furthermore to a two-phase fcc microstructure.

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The effect of modification of benzoylferrocene periphery on catalytic activity toward drying of alkyd resins has been investigated by the combination of experimental techniques. A series of substituted ferrocenes have been synthesized and characterized by analytical and spectroscopic tools including X-ray diffraction analysis on single crystals. The electrochemical behavior of the ferrocene derivatives has been elucidated by cyclic voltammetry and rotation disk voltammetry. The activity toward room temperature curing of alkyd resin has been evaluated by standard mechanical tests on coated plates, which enabled to establish a structure/catalytic activity relationship. Fast drying of test coatings has been observed for formulations of (3-methoxybenzoyl) ferrocene. Time-resolved infrared spectroscopy in combination with attenuated total reflectance sampling technique enabled to reveal the kinetic origin of the improved performance for this ferrocene derivative.

In this paper the development of a new y'/ Y'-alloy on the basis of Alloy718 is presented, where the microstructure is stable at 800°C, mechanical properties are similar to Alloy718, yet do not deteriorate beyond 650°C, and the forging window is wider than the one of Alloy718, allowing for good workability. This was essentially achieved by the addition of about 17%-30% Co in combination with an Al/Ti-ratio of more than 5.0 and an Al-content of about 1.6%-2.2%. The key role of cobalt is to stabilize the 5-phase, allowing for solvus temperatures in excess of 1100°C. Consequently, the stability of the y'-phase can be increased by further addition of aluminum. At the same time the Ti-content is reduced to prevent formation of the r-(Ni,Co)3(Ti,Al,Nb) phase. Besides discussion of the alloy development concept, information on microstructure evolution and mechanical properties will be given.

Currently a new generation of relaunchable space transportation system using liquid hydrogen/ liquid oxygen rocket engines is under development. The inner combustion chamber is exposed to extreme thermal loads and environmental attack during starts. To prevent failure of the cooling channels, a thermal barrier coating to provide thermal and oxidation protection could be applied. Thermal barrier coatings are state of the art for gas turbines and this concept should be transferred to copper substrates in rocket engine applications. The thermomechanical loading conditions are quite different from the gas turbine applications as heat fluxes and temperature gradients are much higher while overall service time is much shorter. As a start for optimization of a suitable coating, a material system known for gas turbines is employed. In this work a thermal barrier coating system is applied by atmospheric plasma spraying to the copper-based high strength alloy Cu-1%Cr-0.3%Zr. The bond coat consists of a NiCrAlY alloy, while partially stabilized zirconia is used as a top coat. Spraying parameter optimization for the new substrate is described. The reached coating system is tested in thermal cycling experiments, where no failure of the coating could be detected. In oxidation experiments good environmental protection of the coating is shown.

X-ray structural and spectral analyses, X-ray diffraction topography and metallography were used to study dendrite structure of Al-4 wt % Cu single crystals grown by the Bridgman technique at a rate of 1 mm/min and on seeds with <001> orientation. The single crystals were obtained upon the crystallization of the melt under the action of a pressure and the gravitational-field component directed along the surface of the crystallization front. Non-uniform distribution of copper in the solid solution and the eutectic content has been found in transverse section of single crystals and strong increase in their concentration was observed at the lateral side of the samples in the direction of the gravitational-field component action. Distribution of copper and the eutectic phase depend on pressure.